I've never requested a specific room, but I have made building and/or floor and/or general area requests and they've always been granted.
For example:
At the WL CL, we requested an inner courtyard view and received it.
At CBR we requested a building close to the food court/pool area (this was before they had the option of booking a preferred location) and twice were given Martinique 25, which is in an excellent location, which is now "preferred" and costs a few dollars more per night.
At POR we requested a building in the Alligator Bayou section that was fairly close to the main building/bus stop, and we were given Building #18, which was in a great/convenient location.
At Polynesian lagoon concierge, we knew we'd be in the Hawaii building and in a room facing the lagoon, but we requested the third floor on 3 different trips and on all 3 trips we got it.
At Animal Kingdom Lodge we booked a pool view room and asked for a room that was not too far of a walk, and we were given a room in a good location, very near the elevators and not too far of a walk from the lobby. Our view of the pool was somewhat obstructed by thin trees, but we loved it.
At the Grand Floridian we didn't make any requests because we were standing right there in the lobby, we asked if they had any Magic Kingdom view rooms, and since they did, we took that room and moved from CBR to the GF right then and there. lol We did pay for a lagoon view room, which was the only option at that time with a MK view.
I think the less specific you are, the more likely you'll be to get a room in an area of the resort that you want
